1. Technical Field
The present disclosure is related to power converter, and in particular to, a multi-mode active clamping power converter.
2. Description of Related Art
With the advancement of technology and the rapid development of portable electronic products, more and more attention has been paid to the performance of switching converters and several of their applications. In recent years, due to the major advances in power electronic technology and the development of nanotechnology, and the growing tendency of electronic devices towards slim and light, energy saving, and cost reducing, the internal power converter design should also trend towards slim and light, energy saving, and design cost reducing. The power supply is generally required for every electric appliance, to convert an input power source from a battery or AC main supply into an output power source with specific rating of the electric appliance. As technology advances, it becomes a routine for power supplies to operate more efficiently or have higher conversion efficiency. As known in the art, the conversion efficiency of a power supply is the ratio of the output power from the output power source to the input power from the input power source.
A power conversion system receives an input DC or AC power and converts the input DC or AC power to a/an DC or AC output power, and the DC or AC output power usually has a voltage different from that of the input power. Control of the output power may respond to the output voltage or the output current. A boost converter (also known as step-up converter) is a power converter which has the output voltage greater than the input voltage. The boost converter is a switched mode power including at least a first electrically controlled switch (for example a transistor), at least a first energy-storing element (for example an electric coil) and an auxiliary element (for example a diode or a second electrically controlled switch). Generally, the first electrically controlled switch and the diode are placed between the electric coil and the output end of the boost converter, wherein the current alternately charges the electric coil, in response to turning-off operation of the first electrically controlled switch, and the current is transmitted to a load, in response to turning-on operation of the first electrically controlled switch. When the current is transmitted to the load, the current is flowing through the diode or the second electrically controlled switch. A buck converter (also known as step-down converter) is a power converter which has the input voltage greater than the output voltage. The buck converter is a switched mode power including at least a third electrically controlled switch (for example a transistor), at least a second energy-storing element (for example an electric coil) and an auxiliary element (for example a diode or a fourth electrically controlled switch). Generally, the third electrically controlled switch and the diode are placed between the input power source and the electric coil, wherein the current alternately charges the electric coil, in response to turning-off operation of the third electrically controlled switch, and the electric coil continuously releases energy to the load, in response to turning-on operation of the third electrically controlled switch. When the electric coil releases energy to the load, the diode or the fourth electrically controlled switch is connected to the electric coil in series. A flyback converter is a power converter which has the output voltage greater or less than the input voltage. The flyback converter is a switched mode power including at least an electrically controlled switch, an energy-storing element, and at least an auxiliary element (for example a diode and/or an additional electrically controlled switch). The energy-storing element includes at least an electric coil (especially a transformer), whereby a voltage ratio can increase with an additional advantage of isolation. Generally, a primary winding of the transformer is connected between the electrically controlled switch and the input power source, and a secondary winding of the transformer is connected between the auxiliary element and the output end of the flyback converter. The power converters listed above is for the explanation of some topologies, and the power converters are not limited thereto.
In the low-power applications, the flyback converter is a widely used power circuit, but the flyback converter has the disadvantages as follows. The input current pulse is suffering from electromagnetic interference, and leakage inductance causes the voltage spike. Furthermore, it is difficult for the traditional active clamping single-ended primary inductor converter to perform zero-voltage switching in the whole load range, and thus it is hard to improve the efficiency greatly.